A solar cell element has been known in which a region (reverse conductivity type region) where a reverse conductivity type impurity element is introduced is provided in a surface layer portion of a front surface in a one conductivity type semiconductor substrate, in which an anti-reflection film and an electrode in line shape are placed on the region, and in which an electrode is placed on a rear surface of the semiconductor substrate. In Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-512041, a solar cell element is suggested, the solar cell element having a structure (selective emitter structure) in which a content concentration of the reverse conductivity type impurity element is increased in the region where the electrode in line shape is placed in the reverse conductivity type region.
For example, the selective emitter structure is formed as follows. First, a p-type semiconductor substrate is disposed in a heating furnace as the one conductivity type semiconductor substrate. Next, in a state where the semiconductor substrate is heated, gas which contains an n-type impurity element as a reverse conductivity type is supplied to the inside of the heating furnace, and thereby the n-type impurity element is introduced into the surface layer portion of the p-type semiconductor substrate by diffusion. At this time, a first emitter region is formed in the surface layer portion of the p-type semiconductor substrate, and a layer (for example, phosphosilicate glass layer) which is a diffusion source of the n-type impurity element is formed on the first emitter region. When a preset position of the diffusion source is selectively irradiated with laser light, the diffusion source is locally heated, and the n-type impurity element is further introduced into the semiconductor substrate by diffusion. Accordingly, in the region where the electrode in line shape is placed, a second emitter region where a content concentration of the n-type impurity element as the reverse conductivity type is increased is formed.
As another example, one main surface of the p-type semiconductor substrate as the one conductivity type is coated with a paste-formed raw material solution (for example, P2O5) which contains the n-type impurity element as the reverse conductivity type. Subsequently, a heat treatment is performed, thereby forming a reverse conductivity region is formed in the surface layer portion of the p-type semiconductor substrate.